- Burns : journal of the International Society for Burn Injuries
- Published about 8 years ago
Legislation enacted to curb methamphetamine production has only temporarily succeeded. Experiencing a recent increase in burns as a result of the new one-pot method, we compared methamphetamine related burn patients who utilized the previous anhydrous ammonia method of production to current patients who largely used the new one-pot method of production.
By theoretical calculations, the gas-phase SO2 hydration reaction assisted by methylamine (MA) and dimethylamine (DMA) was investigated, and the potential contribution of the hydrated product to new particle formation (NPF) also was evaluated. The results show that the energy barrier for aliphatic amines (MA and DMA) assisted SO2 hydration reaction is lower than the corresponding that of water and ammonia assisted SO2 hydration. In these hydration reactions, nearly barrierless reaction (only a barrier of 0.1 kcal mol-1) can be found in the case of SO2 + 2H2O + DMA. These lead us to conclude that the SO2 hydration reaction assisted by MA and DMA is energetically facile. The temporal evolution for hydrated products (CH3NH3+-HSO3–H2O or (CH3)2NH2+-HSO3–H2O) in molecular dynamics simulations indicates that these complexes can self-aggregate into bigger clusters and can absorb water and amine molecules, which means that these hydrated products formed by the hydration reaction may serve as a condensation nucleus to initiate the NPF.
We report herein the discovery of methylamine (CH3 NH2 ) induced defect-healing (MIDH) of CH3 NH3 PbI3 perovskite thin films based on their ultrafast (seconds), reversible chemical reaction with CH3 NH2 gas at room temperature. The key to this healing behavior is the formation and spreading of an intermediate CH3 NH3 PbI3 ⋅xCH3 NH2 liquid phase during this unusual perovskite-gas interaction. We demonstrate the versatility and scalability of the MIDH process, and show dramatic enhancement in the performance of perovskite solar cells (PSCs) with MIDH. This study represents a new direction in the formation of defect-free films of hybrid perovskites.
Biomass fires impact global atmospheric chemistry. The reactive compounds emitted and formed due to biomass fires drive ozone and organic aerosol formation, affecting both air quality and climate. Direct hydroxyl (OH) Reactivity measurements quantify total gaseous reactive pollutant loadings and comparison with measured compounds yields the fraction of unmeasured compounds. Here, we quantified the magnitude and composition of total OH reactivity in the north-west Indo-Gangetic Plain. More than 120% increase occurred in total OH reactivity (28 s-1 to 64 s-1) and from no missing OH reactivity in the normal summertime air, the missing OH reactivity fraction increased to ~40 % in the post-harvest summertime period influenced by large scale biomass fires highlighting presence of unmeasured compounds. Increased missing OH reactivity between the two summertime periods was associated with increased concentrations of compounds with strong photochemical source such as acetaldehyde, acetone, hydroxyacetone, nitromethane, amides, isocyanic acid and primary emissions of acetonitrile and aromatic compounds. Currently even the most detailed state-of-the art atmospheric chemistry models exclude formamide, acetamide, nitromethane and isocyanic acid and their highly reactive precursor alkylamines (e.g. methylamine, ethylamine, dimethylamine, trimethylamine). For improved understanding of atmospheric chemistry-air quality-climate feedbacks in biomass-fire impacted atmospheric environments, future studies should include these compounds.
N-nitrosodimethylamine (NDMA), a probable human carcinogen disinfection by-product, has been detected in chloraminated drinking water systems. Understanding its formation over time is important to control NDMA levels in distribution systems. The main objectives of this study were to investigate the role of chloramine species (i.e., monochloramine and dichloramine); and the factors such as pH, sulfate, and natural organic matter (NOM) influencing the formation of NDMA. Five NDMA precursors (i.e., dimethylamine (DMA), trimethylamine (TMA), N,N-dimethylisopropylamine (DMiPA), N,N-dimethylbenzylamine (DMBzA), and ranitidine (RNTD)) were carefully selected based on their chemical structures and exposed to varying ratios of monochloramine and dichloramine. All amine precursors reacted relatively fast to form NDMA and reached their maximum NDMA yields within 24 h in the presence of excess levels of chloramines (both mono- and dichloramine) or excess levels of dichloramine conditions (with limited monochloramine). When the formation of dichloramine was suppressed (i.e., only monochloramine existed in the system) over the 5 day contact time, NDMA formation from DMA, TMA, and DMiPA was drastically reduced (∼0%). Under monochloramine abundant conditions, however, DMBzA and RNTD showed 40% and 90% NDMA conversions at the end of 5 day contact time, respectively, with slow formation rates, indicating that while these amine precursors react preferentially with dichloramine to form NDMA, they can also react with monochloramine in the absence of dichloramine. NOM and pH influenced dichloramine levels that affected NDMA yields. NOM had an adverse effect on NDMA formation as it created a competition with NDMA precursors for dichloramine. Sulfate did not increase the NDMA formation from the two selected NDMA precursors. pH played a key role as it influenced both chloramine speciation and protonation state of amine precursors and the highest NDMA formation was observed at the pH range where dichloramine and deprotonated amines coexisted. In selected natural water and wastewater samples, dichloramine led to the formation of more NDMA than monochloramine.
Ammonia and amines are important common trace atmospheric species that can enhance new particle formation (NPF) in the Earth’s atmosphere. However, the synergistic effect of these two bases involving nucleation is still lacking. We studied the most stable geometric structures and thermodynamics of quaternary (NH3)(CH3NH2)(H2SO4)m(H2O)n (m = 1-3, n = 0-4) clusters at the PW91PW91/6-311++G(3df,3pd) level of theory for the first time. We find that the proton transfer from H2SO4 molecule to CH3NH2 molecule is easier than to NH3 molecule in the free or hydrated H2SO4-base clusters, and thus leads to the stability. The energetically favorable formation of the (NH3)(CH3NH2)(H2SO4)m(H2O)n (n = 0-4) clusters, by hydration or attachment of base or substitution of ammonia by methylamine at 298.15 K, indicate that ammonia and methylamine together could enhance the stabilization of small binary clusters. At low RH and an ambient temperature of 298.15 K, the concentration of total hydrated (NH3)(CH3NH2)(H2SO4)2 clusters could reach that of total hydrated (NH3)(H2SO4)2 clusters, which is the most stable ammonia-containing cluster. These results indicate that the synergistic effect of NH3 and CH3NH2 might be important in forming the initial cluster with sulfuric acid and subsequently growth process. In addition, the evaporation rates of (NH3)(CH3NH2)(H2SO4)(H2O), (NH3)(CH3NH2)(H2SO4)2 and (NH3)(CH3NH2)(H2SO4)3 clusters, three relative abundant clusters in (NH3)(CH3NH2)(H2SO4)m(H2O)n system, were calculated. We find the stability increases with the increasing number of H2SO4 molecules.
Hybrid organic-inorganic perovskites possess promising signal transduction properties which can be exploited in a variety of sensing applications. Interestingly, the highly polar nature of these materials, while being a bane in terms of stability, can be a boon for sensitivity when they are exposed to polar gases in a controlled atmosphere. However, signal transduction during sensing involves irreversible changes in chemical and physical structure, which is one of the major lacuna preventing its utility in commercial applications. In the context of perovskite materials utilized for sensing, we address major issues such as reversibility of structure and properties, the correlation between instability and structure of the alkylamine, and the relation between packing of alkylammonium chain inside the crystal lattice with the response time towards NH3 gas. The current investigation highlights that volatility of alkylamine formed in presence of NH3 determine the reversibility and stability of original perovskite lattice. In addition, packing of alkylammonium chain inside the perovskite crystal lattice decides the rapid response towards NH3 gas. This mechanistic study addressing three important determining factors such as quick response, reversibility, and high stability, ultimately leads to the design of a stable and sensitive 2D hybrid perovskite towards ammonia sensing.
In this work, we have studied computationally the N-demethylation reaction of methylamine, dimethylamine and trimethylamine as archetypal examples of primary, secondary and tertiary amines catalyzed by high field low spin Fe-containing enzymes such as cytochromes P450. Using DFT calculations, we have obtained that the expected C-H hydroxylation process is achieved for trimethylamine. When dimethylamine and methylamine were studied, two different reaction mechanisms (C-H hydroxylation and a double hydrogen atom transfer) were computed to be energetically accessible and both are equally preferred. Both processes lead to the formation of formaldehyde and the N-demethylated substrate. Finally, as an illustrative example, the relative contribution of the three primary oxidation routes of tamoxifen is rationalized through energetic barriers obtained from density functional calculations and docking experiments involving CYP3A4 and CYP2D6 isoforms. We have found that the N-demethylation process is the intrinsically favored one, whereas other oxidation reactions require most likely preorganization imposed by the residues close to the active sites.
Sulfate aerosols' cooling effect on the global climate has spurred research to understand their mechanisms of formation. Both theoretical and laboratory studies have shown that the formation of sulfate aerosols is enhanced by the presence of a base like ammonia. Stronger alkylamine bases such as monomethylamine (MMA), dimethylamine (DMA) and trimethylamine (TMA) further increase aerosol formation rates by many orders of magnitude relative to that of ammonia. However, recent lab measurements have found that presence of ammonia and alkylamines together increases nucleation rates by another 1-2 orders of magnitude relative to the stronger alkylamines alone. This work explores that observation by studying the thermodynamic stability of clusters containing up to two sulfuric acids and two bases of the same or different type. Initial configurational sampling is performed using genetic algorithm (GA) interfaced to semi-empirical methods to find a large number of low energy configurations. These structures are then subject to quantum mechanical calculations using PW91, M06-2X and ωB97X-D functionals and MP2 with large basis sets. The thermodynamics of formation is reviewed to determine if it rationalizes why mixed base systems yield higher rates of aerosol formation than single base ones. The gas phase basicity of the bases in a cluster is the main determinant of binding strength in smaller clusters such as those in the current study while aqueous phase basicity is more important for larger particles. Besides thermodynamic considerations, the differences in aerosol formation mechanisms as a function of size, and between the gas and particle phases are discussed.
Although currently unregulated, atmospheric ultrafine particles (<100 nm) pose risks for health due to e.g. their capability to penetrate deep into the respiratory system. Ultrafine particles, often minor contributors to atmospheric particulate mass, typically dominate aerosol particle number concentrations. We simulated the response of particle number concentrations over Europe to recent estimates of future emission reductions of aerosol particles and their precursors. We used the chemical transport model PMCAMx-UF, with novel updates including state-of-the-art descriptions of ammonia and dimethylamine new particle formation (NPF) pathways and the condensation of organic compounds onto particles. These processes had notable impacts on atmospheric particle number concentrations. All three emission scenarios (current legislation, optimized emissions, and maximum technically feasible reductions) resulted in substantial (10-50%) decreases in median particle number concentrations over Europe. Consistent reductions were predicted in Central Europe, while Northern Europe exhibited smaller reductions or even increased concentrations. Motivated by the improved NPF descriptions for ammonia and methylamines, special focus was placed on the potential to improve air quality by reducing agricultural emissions, which are a major source of these species. Agricultural emission controls showed promise in reducing ultrafine particle number concentrations, although the change is non-linear with particle size.